1. Field of the Invention
The present invention relates generally to stereolithography and, more specifically, to the use of stereolithography in forming multicomponent mechanical and electro mechanical structures including seamless packaging or encapsulation.
2. State of the Art
In the past decade, a manufacturing technique termed xe2x80x9cstereolithography,xe2x80x9d also known as xe2x80x9clayered manufacturing,xe2x80x9d has evolved to a degree where it is employed in many industries.
Essentially, stereolithography, as conventionally practiced, involves utilizing a computer to generate a three-dimensional (3-D) mathematical simulation or model of an object to be fabricated, such generation usually being effected with 3D computer-aided design (CAD) software. The model or simulation is mathematically separated or xe2x80x9cslicedxe2x80x9d into a large number of relatively thin, parallel, usually vertically superimposed layers, each layer having defined boundaries and other features associated with the model (and thus the actual object to be fabricated) at the level of that layer within the exterior boundaries of the object. A complete assembly or stack of all of the layers defines the entire object, and surface resolution of the object is, in part, dependent upon the thickness of the layers.
The mathematical simulation or model is then employed to generate an actual object by building the object, layer by superimposed layer. A wide variety of approaches to stereolithography by different companies has resulted in techniques for fabrication of objects from both metallic and nonmetallic materials. Regardless of the material employed to fabricate an object, stereolithographic techniques usually involve disposition of a layer of unconsolidated or unfixed material corresponding to each layer within the object boundaries, followed by selective consolidation or fixation of the material to at least a semisolid state in those areas of a given layer corresponding to portions of the object, the consolidated or fixed material also at that time being substantially concurrently bonded to a lower layer. The unconsolidated material employed to build an object may be supplied in particulate or liquid form, and the material itself may be consolidated or fixed or a separate binder material which may be employed to bond material particles to one another and to those of a previously-formed layer. In some instances, thin sheets of material may be superimposed to build an object, each sheet being fixed to a next-lower sheet and unwanted portions of each sheet removed, a stack of such sheets defining the completed object. When particulate materials are employed, resolution of object surfaces is highly dependent upon particle size, whereas when a liquid is employed, surface resolution is highly dependent upon the minimum surface area of the liquid which can be fixed and the minimum thickness of a layer which can be generated. Of course, in either case, resolution and accuracy of object reproduction from the CAD file is also dependent upon the ability of the apparatus used to fix the material to precisely track the mathematical instructions indicating solid areas and boundaries for each layer of material. Toward that end, and depending upon the layer being fixed, various fixation approaches have been employed, including particle bombardment (electron beams), disposing a binder or other fixative (such as by ink-jet printing techniques), or irradiation using heat or specific wavelength ranges.
An early application of stereolithography was to enable rapid fabrication of molds and prototypes of objects from CAD files. Thus, either male or female forms on which mold material may be disposed might be rapidly generated. Prototypes of objects may be built to verify the accuracy of the CAD file defining the object and to detect any design deficiencies and possible fabrication problems before a design was committed to large-scale production.
In more recent years, stereolithography has been employed to develop and refine object designs in relatively inexpensive materials, and has also been used to fabricate small quantities of objects where the cost of conventional fabrication techniques is prohibitive for same, such as in the case of plastic objects conventionally formed by injection molding. It is also known to employ stereolithography in the custom fabrication of products generally built in small quantities or where a product design is rendered only once. Finally, it has been appreciated in some industries that stereolithography provides a capability to fabricate products, such as those including closed interior chambers or convoluted passageways, which cannot be fabricated satisfactorily using conventional manufacturing techniques. It has also been recognized in some industries that a stereolithographic object or component may be formed or built around another, pre-existing object or component to create a larger product.
However, to the inventors"" knowledge, stereolithography has yet to be applied to mass production of tiny articles in volumes of thousands or millions, where the article comprises a micromachine housing/support structure ordinarily requiring assembly of separate parts with associated intermediate seams, gaskets, and other sealing elements, and where extremely high resolution and a high degree of reproducibility of results is required.
The continuing race toward increased miniaturization in the electronic industry is well known, particularly in the manufacture of semiconductor devices. Technology relating to a parallel miniaturization of peripheral electronic equipment has not been developing at the same rate. Thus, for example, while the density of memory devices has greatly increased, making very small memory devices such as memory disks possible, the development of reliable read/write equipment for such memory devices is lagging.
A recently developed type of read/write drive system has been called a xe2x80x9cwobble-motor-microactuator,xe2x80x9d several forms of which are described in U.S. Pat. No. 5,093,594 of Mehregany and U.S. Pat. No. 5,805,375 of Fan et al. One of the difficulties with micromachines is that because of their moving parts and very low power, they are sensitive to any moisture or dust particle and require some sort of protection, particularly when mounted on a circuit board or other substrate material. An object of the present invention is to present a process for forming an effective protective/support structure for a micromachine, which protective/support structure is inexpensive to produce, may be repeatably produced with precision in large batches, and is adaptable to a wide variety of micromachine configurations and sizes.
The present invention provides a method for fabricating micromachines using a stereolithographic (STL) structure-forming technique to form a housing of consecutively polymerized layers. The first layer is formed on a workpiece support substrate or platform and each subsequent layer formed atop the previous layer. A monolithic housing and support for a machine may be rapidly and precisely formed, wherein preformed machine components such as rotating shafts, actuators, electrical leads, etc. are accurately placed within or through the housing walls. The housing may be formed to be absolutely seamless and imperforate, except for machine elements or openings extending through one or more walls of the housing. The housing is a single part or unitary structure, unlike conventional-multiple-part micromachine housings. The housing may include interior machine supports, dividing walls and partitions, shelves, and the like, as will best serve the design and purpose of the micromachine. The housing structure may include elements of planar and/or curved configuration.
The present invention employs computer-controlled, 3D CAD initiated, stereolithographic techniques to form housing/support structures for miniaturized machine assemblies commonly termed xe2x80x9cmicromachinesxe2x80x9d such as, for example, controller micromotors, gearboxes, and the like, such micromachines having overall exterior dimensions on the order of, for example and not by way of limitation, about 5-100 mm. The stereolithographic apparatus may be configured for production of one or more, or even a large number of such micromachines during each STL operation.
The present method preferably includes the use of machine vision to precisely place micromachine components within housing/supports as they are formed, and precisely form the features of the housing/supports, e.g., partitions, shaft holes, bearings, contact surfaces, shelves, projections, etc., to support and house the micromachine components or assemblies of same within a seamless structure.
In a preferred embodiment, an exterior housing/support structure for a micromachine in accordance with the invention is fabricated using precisely focused electromagnetic radiation in the form of an ultraviolet (UV) wavelength laser under control of a computer and responsive to input from a machine vision system such as a pattern recognition system to fix or cure a liquid material in the form of a photopolymer.